Abstract
A semi-closed solar collector greenhouse was tested to evaluate the yield and the energy saving potential compared with a commercial greenhouse. As such, new algorithm for ventilation, carbon dioxide (CO2) enrichment, as well as for cooling and heating purposes initiated by a heat pump, cooling fins under the roof and a low temperature storage tank were developed. This cooling system showed that the collector greenhouse can be kept longer in the closed operation mode than a commercial one resulting in high levels of CO2 concentrations, relative humidity and temperatures. Based on these conditions, the photosynthesis and associated CO2 fixations within the plant population were promoted during the experiment, resulting in a yield increase by 32%. These results were realized, although the mean light interception by energy screens and finned tube heat exchangers was increased by 11% compared to the reference greenhouse. The energy use efficiency was improved by 103% when the collector greenhouse was considered as energy production facility. In this context, the energy saving per kilogram produced tomatoes in the collector greenhouse is equivalent to the combustion of high amounts of different fossil fuels, where the reduced CO2 emissions ranged between 2.32 kg and 4.18 kg CO2 per kg produced tomatoes. The generated total heat was composed of approximately one-third of the latent heat and over two-thirds of the sensible heat, where a maximum collector efficiency factor of 0.7 was achieved.
Highlights
Producers transferred field grown tomatoes to greenhouses in order to improve yield, to reduce phytosanitary problems and to extend the harvest season
The objectives of this study were to improve the CO2 fixation within the crop, the total yield, the energy use efficiency (EUE) and an associated reduction in CO2 emissions using a semi-closed greenhouse, which was controlled by new algorithm for cooling and heating purposes initiated by a heat pump, as well as for ventilation and CO2-enrichment
The energy caused by the transmitted solar radiation and water vapour was captured using a cooling fin system under the roof, which was connected to a reversible heat pump and a low temperature storage tank
Summary
Producers transferred field grown tomatoes to greenhouses in order to improve yield, to reduce phytosanitary problems and to extend the harvest season. The energy consumption in Dutch greenhouses, for instance, accounts for 79% of the energy used in the agricultural sector and 7% of the total energy use in the Netherlands (Lansink & Bezlepkin, 2003) These dimensions show that the growth of greenhouse horticulture production contributes to a large proportion of carbon dioxide (CO2) emissions, which are jointly responsible for the predicted mean global temperature increase (WBGU, 2008). Based on these facts, scientists invested much effort into the development of approaches for using renewable energies, in order to reduce the consumption of fossil fuels for greenhouse heating. The solar radiation sum impinging on the earths surface in Berlin (52°28 ́02 ́ ́N, 13°17 ́56 ́ ́E) was www.ccsenet.org/jas
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